Geology Reference
In-Depth Information
Figure 2. Layout and section sizes for 10-story MRFs
Ground Motion Suite
no permanent damage to structural members, and
thereby increasing the building performance from
a Life Safety level to an Immediate Occupancy
level under the DBE.
For the regular building, this design process
yielded a requirement for the dampers to provide
an increase in the equivalent viscous damping
ratio from 5% to 37%, necessitating a total added
damping of
C
t
= 812 kNs/cm. Application of the
five damper placement techniques then resulted
in damping distributions over the structure as
shown in Table 2. It can be seen that the stiffness-
proportional approach is the most different from
the others, and that none of the optimisation
schemes results in any damping being added at
the bottom story.
A set of twenty ground motion records were se-
lected from the Pacific Earthquake Engineering
Research Center Next-Generation Attenuation
Relationships strong-motion database (PEER,
2005). The primary selection criteria were the
absence of near-fault characteristics and Eurocode
soil B classification (Table 3). Ground motions
were normalised to the same hazard level (i.e.
DBE or MCE), so that performance objectives at
specific hazard levels could be evaluated from the
ground motions. This was performed by scaling
the ground motions to the same pseudo-spectral
acceleration (PSA) at the buildings' fundamental
frequencies and 5% inherent damping.
RESULTS AND DISCUSSION
Table 1. Building properties, prior to damper
retrofit
Performance Indicators
Peak Interstory
Drift (%)
Period (sec)
Peak interstory drift, absolute acceleration, and
residual interstory drift were selected as the main
performance indicators. Interstory drift indicates
potential damage to primary structural members,
while absolute floor acceleration corresponds
to damage of building contents and sensitive
Mode
1
Mode
2
Mode
3
FOE
DBE
Regular
0.88
2.20
2.05
0.70
0.38
Irregular
0.99
2.47
2.31
0.93
0.47
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